The present invention relates generally to variable discharge gear pumps and more specifically to a variable discharge gear pumps having energy recovery.
Gear pumps generally include a pair of oppositely rotating gears having an intermeshed area between an inlet and an outlet. The meshing teeth of the gears open on the inlet side filling the pockets and carrying fluid around to the outlet side. The teeth mesh on the outlet side creating a positive pressure and demesh on the inlet side creating a negative pressure. Generally the axes of the pair of gears are fixed and parallel to each other.
Many methods have been used to vary the discharge of gear pumps. These have included: (a) adjustment of the inlet or outlet structure to determine when compression begins or ends; (b) axial adjustment of the gears relative to each other to adjust the effective axial length of the intermeshing gears; (c) adjustment of the depth of the intermeshing generally via an eccentric; (d) passing fluids to and from the peripheral chambers to vary the throughput; (e) external valves for connecting the inlet and outlet; and (f) the provision of multiple stages with the selectivity of the number of stages used.
In U.S. Pat. No. 1,912,737 to Svenson, radial passages are provided in the gear teeth to communicate the inlet, outlet and meshing areas with a adjustable valve port in the interior of the gears. By adjustment of the valve port, fluid from the outlet is bypassed back to the inlet thereby reducing the discharge of the pump. Because of the size of the radial passages in the gear teeth, the high pressure fluid in the outlet and decreasing displacement meshing area of the teeth force fluid into the interior porting area, and the increasing displacement demeshing area of the meshing teeth and the low pressure inlet draw fluid from the interior valving port. Also, depending upon the speed of the gears, the radial passages become effectively smaller and more restrictive with increased speed.
U.S. Pat. No. 1,985,748 to Svenson shows a similar design to the '737 patent.
U.S. Pat. No. 2,481,646 to Conklin is a typical example of a variable delivery gear pump wherein high pressure fluid from the outlet side is adjustably connected to the pockets of the gear on the inlet side. By adjusting the rectilinear element, the number of pockets that are prefilled with fluid from the outlet side of the pump are selected. This not only bypasses fluid from the outlet to the inlet, but also provides it directly at the open pockets and therefore varies the throughput.
Although these three patents are examples of variable delivery gear pumps wherein the axes of the parallel gears are fixed and fluid is fed back from the output to the input, they fail to recognize the ability to recover energy and substantially reduce the amount of torque needed to drive the gear pump. The specific location of the introduction of the outlet fluid to the inlet fluid, outside the meshing area of Conklin, prevents the use of the high pressure outlet fluid in an area which is capable of recovering energy. The two discussed Svenson patents, although removing fluid from the meshing and providing fluid to the demeshing area of the gears, as well as providing a bypass of outlet fluid to the inlet, the structure of the fluid passages are such that they fail to provide high pressure fluid at the demeshing area of the intermeshing teeth and therefore also does not recover energy.
U.S. Pat. No. 3,669,577 to Swanson is an example of a variable displacement gear pump wherein the gears move axially relative to each other to vary the displacement. This patent also includes radial channels in the teeth of the gears to receive fluid from the inlet chamber and to propel it under centrifugal force into the opening areas on the demeshing gear side to relieve the vacuum of the demeshing gears to thereby reduce vaporization and consequently improve the efficiency of the pump. These channels are not used to effect the displacement of the pump, nor recover energy since the fluid in the channels of the gears are cut off from the high pressure outlet fluid.
Therefore, there exists a need for a variable discharge gear pump of the fixed axis design which includes variable energy recovery.
Thus it is an object of the present invention to provide a variable discharge gear pump having fixed gear displacement which includes energy recovery.
Another object of the present invention is to provide a variable discharge gear pump having variable energy recovery.
A still further object of the present invention is to provide a variable discharge gear pump and energy recovery with a minimum number of parts.
An even further object of the present invention is to provide a large capacity pump which has the reduced loading of smaller capacity pumps.
These and other objects of the invention are attained by providing an adjustable spool in fluid communication with the outlet chamber for adjustably providing pressurized fluid from the outlet chamber to selected portions of the demeshing area of the intermeshing teeth which are between the inlet and outlet chambers to vary the discharge flow of the pump and the amount of energy recovery. This results in maintaining a positive pressure in selected portions of the meshing area as well as equalizing the pressure in the selected areas to the pressure in the outlet chamber. The channel in the spool connecting the outlet and the intermeshing areas is of sufficient dimension to assure that sufficient fluid of high pressure is provided in selected portions of the demeshing area of the gears. This channel is a recess, slot or undercut in the spool which is in continuous communication with the outlet chamber. The spool is positioned rectilinearly along an axis to align the slot in communication with the selected portions of the intermeshing areas. The width of the slot is substantially equal to the height of the teeth of the gears so as to overlap teeth in the intermeshing area and not reduce the pressure available from the outlet chamber. The axis of rectilinear movement of the spool is perpendicular to the plane of the parallel axis of rotation of the pair of gears and is equidistant from the parallel axis. The slot extends from the outlet chamber and over contiguous portions of the meshing and demeshing areas as adjusted. The required torque is reduced by using the high pressure outlet energy to minimize the pressure differential between the meshing and demeshing areas of the intermeshing gear teeth.
Pressurizing the inlet meshing area also helps pressure balance the gears reducing mechanical torque, journal loading and heat during the discharge flow reduction.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.